Buggy code:
public class JExtratorFiles { private JFrame frame ; private JMenuBar menuBar ; private JMenu indexarMenu ; private JMenu buscarMenu ; private JMenu conteudoMenu ; private JMenu metadadosMenu ; private JMenuItem indexarMenuItem ; private JMenuItem buscarMenuItem ; private JMenuItem conteudoMenuItem ; private JMenuItem metadadosMenuItem ; private JButton salvarButton ; private JButton limparButton ; private JTextArea conteudoPainel ; private JScrollPane scrollPainel ; private SelecionarActionListener selecionarListener ; private BotoesActionListener botoesListener ; public JExtratorFiles ( ) { } private void prepareGUI ( ) { frame = new JFrame ( "Extractor<seq2seq4repair_space>Files" ) ; selecionarListener = new SelecionarActionListener ( this ) ; botoesListener = new BotoesActionListener ( this ) ; menuBar = new JMenuBar ( ) ; indexarMenu = new JMenu ( "Indexar" ) ; indexarMenuItem = new JMenuItem ( "Selecionar..." ) ; indexarMenuItem . addActionListener ( selecionarListener ) ; indexarMenu . add ( indexarMenuItem ) ; buscarMenu = new JMenu ( "Buscar" ) ; buscarMenuItem = new JMenuItem ( "Selecionar..." ) ; buscarMenuItem . addActionListener ( selecionarListener ) ; buscarMenu . add ( buscarMenuItem ) ; conteudoMenu = new JMenu ( "Conteúdo" ) ; conteudoMenuItem = new JMenuItem ( "Selecionar..." ) ; conteudoMenuItem . addActionListener ( selecionarListener ) ; conteudoMenu . add ( conteudoMenuItem ) ; metadadosMenu = new JMenu ( "Metadados" ) ; metadadosMenuItem = new JMenuItem ( "Selecionar..." ) ; metadadosMenuItem . addActionListener ( selecionarListener ) ; metadadosMenu . add ( metadadosMenuItem ) ; menuBar . add ( indexarMenu ) ; menuBar . add ( buscarMenu ) ; menuBar . add ( conteudoMenu ) ; menuBar . add ( metadadosMenu ) ; frame . setJMenuBar ( menuBar ) ; conteudoPainel = new JTextArea ( ) ; conteudoPainel . setLineWrap ( true ) ; conteudoPainel . setWrapStyleWord ( true ) ; conteudoPainel . setText ( "Bem<seq2seq4repair_space>vindo<seq2seq4repair_space>ao<seq2seq4repair_space>Extractor<seq2seq4repair_space>Files<seq2seq4repair_space>1.0..." ) ; conteudoPainel . setAutoscrolls ( true ) ; scrollPainel = new JScrollPane ( conteudoPainel ) ; <START_BUG> frame . add ( scrollPainel , BorderLayout . CENTER ) ; <END_BUG> salvarButton = new JButton ( "Salvar" ) ; salvarButton . addActionListener ( botoesListener ) ; limparButton = new JButton ( "Limpar" ) ; limparButton . addActionListener ( botoesListener ) ; JPanel painelButtons = new JPanel ( new FlowLayout ( ) ) ; painelButtons . add ( limparButton ) ; painelButtons . add ( salvarButton ) ; frame . add ( painelButtons , BorderLayout . SOUTH ) ; frame . setDefaultCloseOperation ( JFrame . EXIT_ON_CLOSE ) ; frame . setPreferredSize ( new Dimension ( 700 , 500 ) ) ; frame . pack ( ) ; frame . setLocationRelativeTo ( null ) ; frame . setVisible ( true ) ; } public JMenuItem getIndexarMenuItem ( ) { } public JMenuItem getBuscarMenuItem ( ) { } public JMenuItem getConteudoMenuItem ( ) { } public JMenuItem getMetadadosMenuItem ( ) { } public JTextArea getConteudoPainel ( ) { } public JButton getSalvarButton ( ) { } public JButton getLimparButton ( ) { } }

Fix:
frame . add ( scrollPainel ) ;